Method and device for treatment of products in gas-discharge plasma

ABSTRACT

A method for treatment of products in gas-discharge plasma consists in that a two-step vacuum-arc discharge is initiated between an anode (3) and an integrally cold cathode (2), featuring a metal-gaseous step of plasma and a gaseous step of plasma. The gaseous step of plasma is established by ionizing the working gas with electrons separated from the metal-gaseous step of plasma. Then a product (5) under treatment is preheated to working temperature and held in a preset temperature range. To this end, provision is made in the device for a means (13) for electron separation from the metal-gaseous step of plasma, which means is situated in the zone of the integrally cold cathode (2) and is impermeable to the metal ions generated by the cathode (2). In a particular case the means (13) is made as a set of V-shaped plates (14).

TECHNICAL FIELD

The present invention relates in general to methods and devices forhardening of tools and machine components and more specifically tomethods and devices for treatment of products in gas-discharge plasma.

BACKGROUND ART

Known in the art is a method for treatment of products in gas-dischargeplasma, said discharge being established in the working space betweenthe anode and cathode under a reduced reaction gas pressure, comprisingpreheating of the product to working temperature and holding it attemperatures within a preset range (cf. "Chemical heat treatment ofmaterials" by Yu. Lakhtin et al., 1985, Metallurgia PH, Moscow, pp.177-181 (in Russian).

In the method mentioned above gas-discharge plasma is built up with theaid of a glow discharge at a partial pressure of the reaction gas in therange of 10 to 1000 Pa. Used as the reaction gas most commonly isnitrogen, therefore the method is called ionic nitriding. The process ofionic nitriding involves initiation of an anomalous glow dischargebetween the product (cathode and the anode, the interelectrode voltagebeing from 400 to 1000 V. Virtually the entire potential drop in a glowdischarge is concentrated at the cathode in the region of cathodepotential drop. The ions of the reaction gas (nitrogen) are acceleratedin the region of cathode potential drop so as to bombard the surface ofthe product under treatment, thus heating said surface andsimultaneously diffusing depthward to form a hardened superficial layer.

However, bombardment of the surface of the product under treatment withhigh-energy ions of the reaction gas carried out during ionchemicaltreatment results in the so-called cathode sputtering of the surface ofthe product being treated and hence in deterioration of the initialquality of surface finish.

Inasmuch as the process is conducted at a relatively high voltage(400-1000 V) applied to the product being treated, glow discharge islikely to turn into arc discharge (which is most possible to occur atthe initial stages of the process). Cathode spots of arc discharge causeerosion of the surface of the product being treated in still higherdegree than cathode sputtering. Arcing is reduced by gradual conductingof the process (that is, by reducing the discharge current and voltage).This measure, however, affects throughput capacity. A device forcarrying said method into effect and aimed at treatment of products ingas-discharge plasma is known to comprise a direct current sourceelectrically connected to the cathode and anode (cf. "Chemical heattreatment of materials" by Yu. M. Lakhtin et al., 1985, Metallurgia PH,Moscow, pp. 177-181 (in Russian).

Used as the anode in said device is a chamber in which the product beingtreated is placed, while the cathode is said product itself.

The direct current source enables the voltage to be infinitely adjustedwithin 1000 V.

The working chamber communicates with a pump to build up vacuum and withthe source of the reaction gas which establishes a pressure of 10 to1000 Pa in the chamber.

Once a voltage has been applied to the electrodes, i.e., the cathode andanode, a glow discharge is initiated in the chamber, whereby the product(cathode) is subjected to bombardment with the ions of the reaction gas.As a result, the product is heated and its surface is saturated with theions of the reaction gas, thus hardening the surface layer of theproduct. However, ion bombardment sputters away the surface layer andhence deteriorates the initial quality of surface finish.

One more state-of-the-art method for treatment of products in the plasmaof a gas-discharge established between the anode and cathode at areduced reaction gas pressure is known to comprise preheating of theproduct to working temperature and holding it at temperatures within apreset range (FI, A, 63, 783).

According to said method, gas-discharge plasma is established with theuse of a glow discharge.

The method comprises preheating of the product (cathode) placed in theworking chamber (anode) containing the reaction gas (a nitrogen-oxygenmixture) to 400°-580° C., followed by holding the product at saidtemperature. In view of intensifying the preheating process andincreasing the microhardness of the diffusion layer, chemical heattreatment is carried out at a pressure from 0.13 to 13.0 Pa, and theglow discharge is intensified by electrons accelerated to 200 eV.

Since said method is carried out in glow-discharge plasma and theproduct being treated serves as the cathode, its surface subjected toion bombardment is sputtered away which affects adversely the initialquality of surface finish.

Still more method for treatment of products in gas-discharge plasma isknown to comprise initiation of a vacuum-arc discharge between the anodeand the integrally cold cathode, a vacuum-plasma treatment of theproduct by heating it to working temperature and holding the product ina preset temperature range in the medium of the reaction gas (U.S. Pat.No. 4,734,178).

According to said method, gas-discharge plasma is built up with the useof a more powerful (compared with glow discharge) vacuum-arc dischargeinvolving an integrally cold cathode. A peculiar feature of this methodresides in that the product under treatment heated by being bombardedwith metal ions. However, treatment of heavy-weight products involves aprolonged heating time which is enough for the product surface issputtered away, thus deteriorating the initial quality of surfacefinish.

Moreover, it is due to a low efficiency of the heating procedure thatonly a relatively low-weight product can be treated, this being onaccount of a discordance between the time of an optimum radiation doseand the heating time in case of treating heavy-weight products, whichnarrows the process capabilities of the method as a whole.

A device for treatment of products in gas-discharge plasma is known tocarry out the method discussed before, said device comprising: a sourceof direct current electrically connected to an integrally cold cathodeand to an anode, both being enclosed in a vacuum chamber containing thereaction gas at a reduced pressure (U.S. Pat. No. 4,734,178).

In the device mentioned above the product under treatment is heated bymetal ions generated by the cathode, which results in sputtering awaythe surface of the product and hence in a deteriorated initial qualityof surface finish.

In addition, said device cannot be used for all-over treatment ofproducts, nor can it perform efficient treatment of dielectric products,which to a great extent restricts its technological capacities.

DISCLOSURE OF THE INVENTION

The present invention has for its principal object to provide a methodfor treatment of products in gas-discharge plasma, according to whichsuch a vacuum-arc discharge is initiated that makes it possible toretain the initial quality of surface finish of the product beingtreated and to extend the process capabilities, as well as to provide adevice for treatment of products in gas-discharge plasma, which carriessaid method into effect and wherein provision is made for such a meansthat makes it possible to extend the process capabilities of the deviceand to preserve the initial quality of surface finish of said product.

The foregoing object is accomplished due to the fact that in a methodfor treatment of products in gas-discharge plasma, comprising initiationof a vacuum-arc discharge between the anode and the integrally coldcathode a vacuum-plasma treatment of the product by preheating it toworking temperature and holding the product in a preset temperaturerange in the medium of a working gas, according to the invention, atwo-stage vacuum-arc discharge is initiated between the anode and theintegrally cold cathode, said discharge featuring a metal-gaseous stepof plasma and a gaseous step of plasma, i.e., the gaseous discharge,both of said steps being isolated from each other, while the latter stepis established by ionizing the working gas with electrons separated fromthe metal-gaseous step of plasma of said vacuum-arc discharge.

The plasma of the vacuum-arc discharge can be generated at reducedworking gas pressure in the range of 10⁻² to 10 Pa.

It is advisable that the vacuum-plasma treatment of the product byexposing it to the main preheating to working temperature and holding ina preset temperature range be effected at the gaseous step of the vacuumarc discharge plasma.

It is expedient that the product under treatment, while being subjectedto the main preheating, be additionally treated with a directionalaccelerated beam.

It is quite reasonable that nitrogen be used as the working gas.

It is favorable that the main heating of the product under treatment toworking temperature be carried out by applying a positive potential tosaid product.

The main heating of the product under treatment to working temperaturemay also be effected by applying a negative potential to said product.

The main heating of the product being treated to working temperature mayalso be carried out with a floating potential applied to the productunder treatment and initiated by the plasma of the gaseous step of thevacuum-arc discharge.

It is desirable to use a directional beam of neutral particles as thedirectional accelerated beam.

It is appropriate that the product under treatment be held in a presettemperature range by applying a positive potential to said product.

It is advantageous that a positive potential be stepwise applied to theproduct under treatment.

It is quite reasonable that the product under treatment be held in apreset temperature range by applying a negative potential thereto.

It is convenient that the product under treatment be held in a presettemperature range under a floating potential applied thereto and thatsaid potential be initiated by the plasma of the gaseous step of thevacuum-arc discharge.

It is practicable to remove the negative potential from the productunder treatment and to aleenergize the gaseous step of the vacuum-arcdischarge plasma as soon as arc-discharge breakdowns occur on theproduct.

It is effective that the holding of the product under treatment in apreset temperature range at the gaseous step of the vacuum-arc dischargeplasma be followed by applying a coating to the surface of said product.

It is convenient that a magnetic field be built up concurrently withapplication of a coating to the surface of the product under treatmentat the gaseous step of the vacuum-arc discharge plasma, the lines offorce of said magnetic field being arranged in planes square with thedirection of the vacuum-arc discharge current.

The object of the invention is accomplished also due to the fact that ina device for treatment of products in gas-discharge plasma for carryingthe aforementioned method into effect and comprising a source of directcurrent electrically connected to an integrally cold cathode and to amain anode, both being enclosed in a vacuum chamber in a medium of theworking gas at a reduced pressure, according to the invention, provisionis made for a means aimed at separation of electrons from themetal-gaseous step of the vacuum-arc discharge plasma, said means beingsituated in the zone of the integrally cold cathode and beingimpermeable to metal ions generated by the integrally cold cathode.

Used as the main anode can be the product under treatment itself.

It is expedient that the device be provided with an additional anode sopositioned with respect to the integrally cold cathode and the means forseparation of electrons as to enable the product under treatment to bearranged between the cathode, the means for electron separation, and theadditional anode, and with a two-way switch connected to both anodes andto the source of direct current.

It is desirable that the means for separation of electrons be shaped asa set of V-form plates facing with one of their side surfaces toward theintegrally cold cathode, and with the other side surface, toward themain anode.

The V-form plates of the means for electron separation can be set inreciprocating motion with respect to the walls of the vacuum chamber.

It is appropriate that the means for electron separation be shaped aslouverboards.

The means for electron separation may be shaped as an iris diaphragmwhose leaves are spaced apart in the zone of overlapping along thelongitudinal axis of the vacuum chamber.

It is favorable that the means for electron separation be made as anL-shaped branch having one of its ends facing toward the main anode,while the integrally cold cathode be located in close proximity to theopposite nozzle end.

It is quite effective that the means for electron separation be in factthe vacuum chamber wall situated in the zone of the integrally coldcathode which is so positioned that its working area faces toward saidwall.

The means for electron separation may be shaped as a disk arranged in aspaced position with respect to the walls of the vacuum chamber.

It is practicable that the integrally cold cathode be so positioned thatits working area be angularly movable through 180° with respect to thevacuum chamber wall which serves as the means for electron separation.

It is worthwhile that the additional anode be shaped as a hollowcylinder one of whose ends faces towards the integrally cold cathode andthe interior thereof accommodates the product being treated and thatprovision be made for a solenoid encompassing the additional anode, anda disk having a center hole and arranged coaxially with the additionalanode between the means for electron separation and the end of theadditional anode in close proximity to both said means and said anode.

It is convenient that provision be made in the present device for asputtering target having a center hole and connected to the negativepole of an individual source of direct current, said target beinginterposed between the means for electron separation and the additionalanode.

The sputtering target may be arranged coaxially with the additionalanode.

It is advantageous that the sputtering target be shaped as a disk havinga center hole.

It is preferable that the additional anode be ring-shaped and thecross-sectional area of said ring-shaped anode be equal to, or in excessof the cross-sectional area of the interior of the center hole in thesputtering target.

The sputtering target may also be shaped as a hollow cylinder whoseinterior is in fact the center hole of the sputtering target.

It is advisable that the sputtering target be shaped as a set of arcuateplates insulated from one another and arranged circumferentially so asto form the center hole of the sputtering target.

Such a realization of the proposed method and such a constructionarrangement of the device carrying said method into effect, according tothe invention, enable treatment of products to be performed withoutaffecting the initial quality of surface finish which in turn makes itpossible to render the heating process and the holding of the product ina preset temperature range the final operation preceding application ofa coating to the surface thus treated without subsequent grinding andpolishing operations, as well as to apply a coating to the surface ofthe product in a continuous technological process in the same vacuumchamber, which extends considerably the process capabilities of themethod and device proposed herein.

In addition, the device, according to the invention for carrying theproposed method into effect adds to the throughput capacity of theproposed method of treatment due to a possibility of heatingheavy-weight products, long-size ones inclusive, as well as provides foran efficient treatment of dielectric products.

BRIEF DESCRIPTION OF THE DRAWINGS

In what follows the invention is illustrated by a detailed descriptionof specific exemplary embodiments thereof with reference to theaccompanying drawings, wherein:

FIG. 1 is a general schematic diagram of the proposed device fortreatment of products in gas-discharge plasma, carrying into effect themethod for treatment of products in gas-discharge plasma, according tothe invention, showing a longitudinal sectional view of the workingchamber of the device;

FIG. 2 is a general schematic diagram of an alternative embodiment ofthe device of FIG. 1;

FIG. 3 is a general schematic diagram of another embodiment of thedevice of FIGS. 1 and 2;

FIG. 4 is a general schematic diagram of one more embodiment of thedevice of FIG. 3;

FIG. 5 is a general schematic diagram of one of the embodiments of thedevice of FIG. 1;

FIG. 6 is a general schematic diagram of still more embodiment of thedevice of FIG. 1;

FIG. 7 is a general schematic diagram of another embodiment of thedevice shown in FIG. 6;

FIG. 8 is a general schematic diagram of one of the embodiments of thedevice as shown in FIGS. 1 and 4;

FIG. 9 is a general schematic diagram of one more embodiment of thedevice according to the invention as shown in FIG. 8;

FIG. 10 is a general schematic diagram of one of the embodiments of thedevice as shown in FIG. 9;

FIG. 11 is a general schematic diagram of one more embodiment of thedevice as shown in FIG. 10;

FIG. 12 is a section taken along the line XII--XII in FIG. 11;

FIG. 13 is a general schematic diagram of one of the embodiments of thedevice, according to the invention, as shown in FIGS. 1 and 4; and

FIG. 14 presents a characteristic curve of microhardness of the nitridedlayer of the product being treated vs. the depth of said layer forhigh-speed tool steel as attained by the device of FIG. 2.

BEST WAYS OF CARRYING OUT THE INVENTION

The method for treatment of products in gas-discharge plasma accordingto the invention, consists in that a two-step vacuum-arc discharge isinitiated between the anode and the integrally cold cathode, avacuum-plasma treatment of the product by its being preheated to workingtemperature and then held in a preset temperature range in the medium ofthe working gas. The two-step vacuum-arc discharge initiated between theanode and the integrally cold cathode has a metal-gaseous step of plasmaand a gaseous step of plasma (gas discharge). The latter step isestablished by ionizing the working gas with electrons separated fromthe metal-gaseous step of plasma of the vacuum-arc discharge. When avacuum-arc discharge is initiated between the integrally cold cathodeand the anode in the presence of the working gas, the interelectrodespace is filled with metal-gas plasma in which metal ions are present,generated by the cathode spot of the vacuum arc, as well as gaseous ionsresulting from the process of metal ion recharging in the interelectrodespace. When separating an electron flow from an ion flow in theinterelectrode space, the electrons separated from the metal-gaseousstep of plasma are accelerated under the effect of the electric fieldgenerated by the anode and ionize the working gas confined in the spacesurrounding the anode.

The aforesaid space is filled with the working gas plasma alone, beingdevoid of metal ions, whereas all the merits of the vacuum-arc dischargeare retained, that is, a strong discharge electron current.

The magnitude of electron current that can be obtained in a vacuum-arcdischarge has a lower limit bound by the minimum stable arcing current(depending on the material of the cathode and the way of cathode spotretention on the cathode, the arcing current may range within 20 and 200A). The upper limit of the discharge current is defined by thethermophysical properties of the cathode being cooled. The cathodeworking surface must not be heated during operation to a temperature atwhich erosion is increased, said temperature depending on the meltingpoint of the material the cathode is made from.

High values of the vacuum-arc discharge electron current result in ahigher degree of ionization of the working gas plasma and hence in ahigher plasma activity.

Moreover, high values of the vacuum-arc discharge current add to theheating capacity of the discharge, which is essential for vacuum plasmatreatment of large-size heavy-weight products.

Gas-discharge plasma is generated at a reduced working gas pressure thatprovides for a stable persistence of a vacuum-arc dischargepredominantly in the range of 10⁻² and 10 Pa.

The pressure range mentioned above is characteristic of an optimumregion of a stable persistence of the vacuum-arc discharge since thevoltage across the discharge electrodes substantially increases when theworking gas pressure is above or below said range, while stability ofdischarge is badly affected due to current pulsation so that thedischarge may spontaneously discontinue for a prolonged period of time.

The vacuum-plasma treatment including preheating of the product toworking temperature and holding in a preset temperature range is carriedout at the gaseous step of the vacuum-arc discharge plasma, preferablyin the medium of nitrogen used as the working gas.

The vacuum-plasma treatment of products at the gaseous step of thevacuum-arc discharge plasma may be performed simultaneously with anadditional treatment of the product with a directional beam ofaccelerated particles, in particular, with a directional beam of neutralparticles, such as molecules of gases, e.g., those of argon. Inasmuch asno potential is applied to the product from an external source duringtreatment with a beam of accelerated particles, an efficient treatmentof dielectric products is practicable, as well as that of metal productswithout leaving the traces of cathode spots thereon, which precludes anyspoilage of the products under treatment due to a substantialdeterioration of the initial quality of surface finish.

Whenever the initial quality of surface finish of the product undertreatment must be preserved, or in case of vacuum-plasma treatment ofproducts having thin-layer coating, wherein etching of the surface isinadmissible due to the danger of complete or partial destruction of thefilm coating, in one of the embodiments of the proposed process,according to the invention, the product under treatment is preheated toworking temperature and held in a preset temperature range in thegas-discharge plasma by applying a positive potential thereto.

When a positive potential is applied to the product under treatmentduring its being preheated and held in a preset temperature range in thegas-discharge plasma, the product is subjected to electron bombardment.It is known commonly that no sputtering of the surface being bombardedoccurs due to a low electron mass, hence the initial quality of surfacefinish is retained. The value of the positive potential applied to thecathode and anode equals to a few scores of volts (as a rule under 100V). The power output of the anode may amount to 60% of a total inputpower applied to the discharge. In addition, no cathode spots are liableto occur on the product to which a positive potential is applied, saidspots being causative of surface erosion of the product under treatment.

The preset temperature range wherein the product under treatment isheld, is maintained by reducing the discharge current to a requiredlevel. If, however, said temperature cannot be maintained at a requiredlevel during reducing the discharge current to the value of a minimumcurrent required for a stable persistence of a vacuum-arc discharge (asa rule, a few scores of Amperes), which is the case with vacuum-plasmatreatment of products having a relatively low weight, the thisembodiment of the proposed method proves to be impracticable.

Whenever the initial quality of surface finish of products having arelatively low weight must be preserved, use may be made of one moreembodiment of the proposed method, according to the invention, whereinthe product under treatment is preheated to working temperature byapplying a positive potential thereto and is held in a presettemperature range in the gas-discharge plasma with a floating potentialacross the product being treated.

The floating potential is accepted by any product placed in plasma andto which no voltage is applied from an external source. It is due tohigh mobility of electrons (compared with ions) that the product getsnegatively charged self-congruently to such a potential as to provide anequal number of the ions and electrons incident thereupon. When theproduct gets cooled due to having been de-energized, it can be reheatedunder a positive potential applied either continuously or intermittentlythereto.

The value of the floating negative potential is inadequately high tocause such an ionic bombardment that results in sputtering of thematerial of the product, since the floating potential in plasma is belowthe threshold of material sputtering.

When preserving of the initial quality of surface finish of aheavy-weight product does not matter but it is necessary to improve theadhesive properties of the products being treated, so the product ispreheated to working temperature by applying a positive potentialthereto and is held in a preset temperature range by applying a negativepotential thereto. Surface irregularities resulting from ionicbombardment, as well as activation of the crystallization nuclei thatoccurs during holding of the product in a preset temperature range undera negative potential contribute to improvement in the adhesiveproperties of the surface of the product under treatment.

When subjected to a vacuum-plasma treatment are products having throughholes, such as sleeves or pipes, the method, according to the invention,provides for preheating of the product to working temperature in thegas-discharge plasma and holding of said product in a preset temperaturerange by applying a negative potential thereto, while the discharge ispassed through the hole in the product. Upon applying a negativepotential to the product gas ions are withdrawn from the gas-dischargedischarge plasma passing through the aforesaid hole, and are acceleratedby bombarding the walls, thus heating them.

Application of a negative potential to the product under treatment maybe accompanied by arc-discharge breakdowns featured by an abrupt currentrise and voltage drop. As a result of such a breakdown the productbecomes the cathode of the vacuum-arc discharge and the cathode spotappear on its surface so that the whole energy of the vacuum-arcdischarge that is generated on the cathode, is concentrated in saidcathode spots. These spots cause erosion of the surface of the productunder treatment, thus deteriorating the initial quality of surfacefinish. To ensure against this phenomenon, the product is relieved fromthe negative potential as soon as an arc discharge breakdown occurs andthe gaseous step of the vacuum-arc discharge plasma is aleenergized. Anyremoval of a negative potential from the product aimed at eliminationarc-discharge breakdowns is not sufficient under conditions of atwo-step vacuum-arc discharge.

This can be explained by the fact that a unipolar vacuum arc can persiston the product placed in gas plasma upon the onset of an arc-dischargebreakdown on the product and disconnection of the power source, sincethe arc can burn without supplying electrons from external sources. Theelectrons are supplied for the arc discharge to persist directly fromgas-discharge plasma due to higher mobility of the electronic componentof the plasma compared with the ion component thereof. Withdrawal ofelectrons from the product is carried out due to electron emission fromthe arc cathode spot to gas-discharge plasma charged positively withrespect to the product.

It must be emphasized that application of a negative potential to theproduct under treatment in the working gas plasma generated according tothe proposed method, is not similar to application of a negativepotential to the product being treated in a glow discharge, inasmuch as,according to the proposed method, the product does not serve as thedischarge cathode and the ions of a more powerful vacuum-arc dischargeare used.

Application of a positive potential to the product having a throughhole, however, fails to solve the problem of obtaining a uniformlyhardened layer of the hole faces, because the discharge does not passthrough the hole and is stricken at the product end nearest to thecathode.

Thus, preheating of products with gaseous ions involving a negativepotential in vacuum-plasma treatment of product having through holes,has not virtually an alternative.

Holding of products in a preset temperature range is carried out byappropriately controlling the intensity of discharge current.

In another embodiment of the proposed method, according to theinvention, wherein subjected to the vacuum-plasma treatment are suchproducts having through holes as sleeves or pipes, the method, accordingto the invention, provides for preheating of the product under treatmentin a preset temperature range in gas-discharge plasma by applying anegative potential to the product under treatment and holding saidproduct in a preset temperature range under a floating potential appliedto the product being treated.

It is expedient that the aforementioned process of holding the productbeing treated by virtue of a floating potential applied thereto becarried out when it is necessary to provide a high-rate vacuum-plasmatreatment, in particular, chemical heat treatment in layers up to 20 μmthick. In such a case the vacuum-arc discharge current is maintained ata maximum level (like in preheating), hence the working gas plasmaexhibits its maximum activity.

In one of the embodiments of the method, according to the invention, theproduct under treatment is preheated to working temperature and held ina preset temperature range in gas-discharge plasma under a floatingpotential applied to said product.

With a floating potential applied to the product under treatment thelatter is heated by virtue of the energy of plasma particles which arenot accelerated due to application of a potential to the product from anexternal source. Energy imparted to the plasma depends on the workinggas pressure, that is, the higher the gas pressure the greater theamount of energy imparted to the gas plasma.

It is expedient that the product under treatment be preheated to workingtemperature and held in a preset temperature range in gas-dischargeplasma under a floating potential applied to said product whenperforming a vacuum-plasma treatment of small-size products under 3 mmin diameter.

Such being the case, the discharge parameters (that is, working gaspressure arc discharge current) determine very neatly the temperature ofthe product, that is why it is necessary to strictly adhere to theaforesaid parameters, whereby the temperature of small-size products maybe left out of observation, while such an observation offers somedifficulties in routine industrial technological processes.

When treating small-size products, in particular, cutting tools havingsharp cutting lips, no overheating of the latter occurs due to anincreased concentration of charged particles that owes its origin tohigher values of electric field intensity close to said cutting lipsupon applying a positive or negative potential to the product undertreatment.

In a general case, apart from the aforedescribed variants of preheatingand holding of the product under treatment, the product may be preheatedby applying a positive potential in a preset temperature range thereto,and be held applying a positive potential stepwise thereto; the productmay be preheated by applying a positive potential thereto and held in apreset temperature range by applying a floating potential to theproduct; preheating of the product is carried out by applying a negativepotential thereto and holding the product in a preset temperature rangeis effected by stepwise application of a positive potential thereto,preheating of the product is effected by applying a negative potentialand holding the product in a preset temperature range is carried out byapplying a positive potential to said product; preheating of the productis performed by applying a floating potential thereto and holding theproduct in a preset temperature range is carried out by applying apositive potential to the product; preheating of the product is carriedout by applying a floating potential thereto and holding of the productin a preset temperature range is carried out by applying stepwise apositive potential to said product, preheating of the product byapplying a floating potential thereto and holding of said product in apreset temperature range by applying a negative potential to saidproduct.

All the variants of realization of the proposed method, according to theinvention, provide for application of a coating to the surface of theproduct in a gaseous step of the vacuum-arc discharge, which follows theprocess of preheating of the product to working temperature and holdingit in a preset temperature range.

According to one of the embodiments of the proposed method, applicationof a coating to the surface of the product being treated is accompaniedby generation of a magnetic field in the gaseous step of the vacuum-arcdischarge plasma, the lines of force of which are arranged in planessquare with the direction of the electron flow of said vacuum-arcdischarge.

The magnetic field developed according to said embodiment of the method,deflects the electron flow that conducts current in the anode-cathodedischarge gap, in a preset direction. As a result, the density of theion current increases and hence the activity of plasma and throughputcapacity of the method, according to the invention, are enhanced, too.

Given below is a detailed description of some specific embodiments ofthe herein proposed device: for treatment of products in gas-dischargeplasma, carrying into effect the method, according to the invention.

The device for treatment of products in gas-discharge plasma accordingto the invention, carrying into effect the proposed method comprises aworking chamber 1 (FIG. 1) which accommodates an integrally cold cathode2, an anode 3, and a holding fixture 4 for a product 5 being treated.

The chamber 1 communicates with a source 6 of working gas and has aconnection 7 communicating with a pump (omitted in the drawing as notbeing the subject of the present invention) for air evacuation from theworking space of the chamber 1 in the direction of the arrow toestablish vacuum therein.

Both the cathode 2 and the anode 3 are connected, via insulators 8 builtinto the walls of the chamber 1, to a source 9 of direct current.

The cathode 2 has a shield 10 which establishes a nonworking area and aworking area 12 of the cathode 2.

Used as the anode 3 is the product 5 being treated.

The chamber 1 accommodates also a means 13 for separating electrons fromthe metal-gaseous step of the vacuum-arc discharge plasma, said meansbeing located in the zone of the integrally cold cathode 2 and beingimpermeable to ions generated by the latter.

In this embodiment of the device, according to the invention, the means13 appears as a set of V-shaped plates 14, their side surface 15 facingtowards the cathode 2, while another surface 16 thereof faces towardsthe product 5.

The means 13 divides the interior space of the chamber 1 intocompartments 17 and 18, of which the latter serves as the working spaceof the chamber 1, while the former compartment is an auxiliary one andserves for electron emission into the compartment 18.

A thermocouple 19 is held to the product 5 being treated and is broughtoutside of the working (vacuum) chamber 1 through an insulator 20 builtinto one of the walls of the chamber 1 to be connected to a temperaturegauge 21 aimed at measuring the temperature of the product 5 undertreatment.

The embodiment of the device discussed above, according to theinvention, is expedient to be used when applying the herein disclosedmethod to large-size heavy-weight products, wherein the amount of heatwithdrawn at the working temperature exceeds the power developed on theanode 3 at a minimum stable arcing current on the cathode 2, when theproduct 5 is preheated and held in a preset temperature range byapplying a positive potential to the product 5, that is, the anode 3.

An embodiment of the device, according to the invention, which carriesinto effect the method proposed herein and is represented in FIG. 2, issimilar to the device of FIG. 1.

The sole difference resides in that the device of FIG. 2 is providedwith an anode 22 which is so positioned with respect to the integrallycold cathode 2 and the means 13 for electron separation that the productunder treatment could be interposed between the cathode 2, the means 13,and the anode 22, a two-way switch 23 connected to the direct-currentsource 9 and to the anode 3 and 22, and a control unit 24 of the two-wayswitch 23, the input of said control unit being electrically connectedto the thermocouple 19, while its output is mechanically associated withthe two-way way switch 23. The anode 22 is electrically isolated fromthe chamber 1 by the insulator 8 built into one of the walls of thechamber.

In the embodiment of the device described herein and carrying intoeffect the method, according to the invention, the means 13 for electronseparation appears as an iris diaphragm whose leaves 25 are spaced apartat a distance "a" from one another in the zone of overlapping along thelongitudinal axis of the vacuum chamber 1 and are actuated with the aidof a crank 26 having a handle 27 and held together with one of theleaves 25, said crank being brought outside the limits of thecompartment 17 of the chamber 1 through a vacuum seal 28.

This embodiment of the device being disclosed herein carries into effectthe method according to the invention in the following cases: when theproduct 5 is preheated and held at a positive potential when preheatingis carried out at a positive potential and holding, at a floatingpotential; and when preheating and holding are carried out at a floatingpotential.

In addition, the embodiment under consideration carries into effect themethod, whereby holding of the product 5 in a preset temperature rangeat the gaseous step of the vacuum-arc discharge plasma is followed byapplying a coating to the surface of the product 5, consisting of acompound of the material of the integral cold cathode 2 with the workinggas, e.g., nitrogen.

An embodiment of the device, according to the invention, presented inFIG. 3 is similar to the device of FIGS. 1 and 2.

A difference consists in that the V-shaped plates 14 (FIG. 3) of themeans 13 are reciprocating with respect to the walls of the chamber 1 inthe direction indicated by arrows B and C. To this aim the chamber 1 isprovided with a socket 29 which accommodates a connecting rod 30provided with a handle 31 and brought outside of the socket 29 through avacuum seal 32 built into the wall of the socket 29. The opposite end ofthe connecting rod 30 is secured together with the plates 14. Thisembodiment of the device proposed herein can find most utility when usedfor adding to the wear-resistance of the products that have passed thevacuum-plasma treatment, in particular, chemical heat treatment, bysubsequently applying a wear-resistant coating to the surface of theproduct, said coating consisting of a compound of the metal from whichthe integrally cold cathode 2 is made, with the working gas, i.e.,nitrogen. As far as the treatment techniques are concerned the presentembodiment of the device differs in nothing from the precedingembodiment as shown in FIG. 2.

An embodiment of the device shown in FIG. 4 for carrying into effect themethod, according to the invention, is similar to the device of FIG. 3.

The sole difference from the preceding embodiment resides in that themeans 13 (FIG. 4) for electron separation is shaped as louverboardswhose slats 33 are connected to the connecting rod 34 provided with thehandle 35 and brought out of the compartment 17 of the working space ofthe chamber 1 through a vacuum seal 36 built into one of the wallsthereof.

The device in question comprises one more source 37 of direct currentwhose negative pole is connected, via a switch 38, to the holdingfixture 4 of the product 5, and its positive pole is connected to thechamber 1.

This embodiment of the device carries into effect the method accordingto the invention, is applicable in cases where the product 5 ispreheated by virtue of a positive potential applied thereto, and is heldin a preset temperature range by applying a negative potential thereto,where the product 5 is preheated and held at a floating potentialapplied thereto, where the product 5 is preheated at a negativepotential and held at a positive potential applied stepwise thereto;where preheating and holding of the product 5 are carried out at anegative potential applied thereto where preheating is effected at anegative potential and holding, at a positive potential applied to theproduct 5; where the heating is performed at a negative potential andholding at a floating potential applied to the product 5; wherepreheating is carried out at a floating potential and holding, at apositive potential applied to the product 5; and where preheating iseffected at a floating potential and holding, at a negative potentialapplied to the product 5.

In addition, this embodiment of the device carries into effect theproposed method whenever the products that have passed the vacuum-plasmatreatment, in particular, chemical heat treatment, are to be coatedsubsequently with a wear-resistant coating aimed at increasing thewear-resistant properties thereof, said coating being in fact thematerial of the cathode 2 or a compound of said material with theworking gas, i.e., nitrogen.

An embodiment of the device shown in FIG. 5 and carrying into effect themethod, according to the invention, is similar to the device of FIG. 1.

The sole difference from the preceding embodiment consists in that themeans 13 (FIG. 5) for electron separation appears as an L-shaped branch39 whose end 40 communicates with the chamber 1 and faces towards theanode 3, whereas the cathode 2 is situated in close proximity to an end41 of said branch 39, the working area 12 of said cathode 2 beinglocated out of the zone of direct optical view of internal walls 12 ofthe chamber 1.

The device of FIG. 5 carries into effect the herein-proposed method,wherein the product 5 is preheated and held in a preset temperaturerange by being energized with a positive potential applied thereto.

It is however obvious that the embodiment of the device with the means13 shaped as the L-shaped branch 39 may he used in the device shown inFIGS. 2, 3, and 4 for carrying out the vacuum-plasma treatment using theprocess techniques inherent in the devices described before and inillustrated FIGS. 2, 3, and 4.

One more embodiment of the device carrying into effect the methoddisclosed herein is presented in FIG. 6.

The embodiment of the device shown in FIG. 6 and carrying into effectthe method, according to the invention, is similar to the device shownin FIG. 1.

The sole difference consists in that serving as the means 13 (FIG. 6)for electron separation is a wall 43 itself of the vacuum chamber 1,said wall being situated in the zone of the integrally cold cathode 2,which is so positioned that its working area 12 faces towards said wall43.

The device shown in FIG. 6 carries into effect the method disclosedherein, wherein the product 5 is preheated and held in a presettemperature range by applying a positive potential thereto.

This embodiment, however, wherein the integrally cold cathode 2 is soarranged that its working area 12 faces oppositely the anode 3 andwherein the corresponding wall of the chamber 1 serves as the means 13,is also applicable in the device of FIGS. 2, 3, and 4.

Another embodiment of the device is shown in FIG. 7 and is similar tothe device of FIG. 6. The sole difference lies with the fact that theintegrally cold cathode 2 (FIG. 7) is so positioned that its workingarea 12 be angularly displaceable through 180° with respect to the wall43 as shown with a dotted line in FIG. 7.

The device shown in FIG. 7 realizes the method disclosed herein,according to which the product 5 is preheated and held in a presettemperature range by being supplied with a positive potential.

An embodiment of the device, according to the invention, as presented inFIG. 8 is similar to the device of FIGS. 1 and 4.

The sole difference is in that the anode 22 (FIG. 8) is shaped as ahollow cylinder 44 having its end 45 facing towards the cathode 2 andwhose interior 46 accommodates a product 47 under treatment appearing asrods held to a fixture 48. The cylinder 44 is encompassed by a solenoid49 situated outside of the chamber 1. A disk 50 provided with a centerhole 51 is accommodated in the chamber 1 and set coaxially with thecylinder 44 between the V-shaped plates 14 of the means 13 and the end45 of the cylinder 44 in close proximity to both.

The device discussed above can be used for intensifying the process ofvacuum-plasma treatment, as well as for realization of the processdisclosed herein in cases where the product 47 under treatment ispreheated to working temperature and held in a preset temperature rangein gas-discharge plasma at a floating potential applied to the product47, as well as where the product 47 is preheated to working temperatureand held in a preset temperature range at a positive potential and afloating potential respectively. In both of the cases mentioned beforeit was expedient that a preset temperature at which the product 47 is tobe held be maintained by stepwise application of a positive potentialthereto.

The device of FIG. 9 is similar to that of FIG. 8.

The sole difference resides in that provision is therein made for asputtering target 52 (FIG. 9) having a center hole 53, said target beinginterposed between the plates 14 of the means 13 and the end 45 of thecylinder 44 and arranged coaxially with the disk 50 and the cylinder 44.

The sputtering target 52 in this embodiment of the device is in fact adisk 54 having the center hole 53.

The sputtering target 52 is connected to the negative pole of anindividual source 55 of direct current through an insulator 56 builtinto the wall of the chamber 1 and has a sputtering surface 57.

The embodiment of the device described above is reasonable to be usedfor intensifying the process of vacuum-plasma treatment, as well as incarrying into effect the proposed method when the product 47 undertreatment is preheated to working temperature and held in a presettemperature range in gas-discharge plasma at a floating potentialapplied thereto, and also when preheating of the product 47 to workingtemperature is carried out at a positive potential and holding of saidproduct is performed at a floating potential applied thereto. In bothcases mentioned above it is expedient that a preset holding temperatureof the product 47 be maintained by stepwise application of a positivepotential thereto.

In addition, the embodiment of the device under consideration can beused for increasing the wear-resistance of the products that have passedthe vacuum-plasma treatment, in particular, chemical heat treatment, bysubsequent application of a wear-resistant coating, consisting of thecompound of the metal from which the sputtering target 52 is made withthe working gas, i.e., nitrogen, or other.

The device of FIG. 10 is similar to that of FIG. 9.

The sole difference resides in that the sputtering target 52 (FIG. 10)appears as a hollow cylinder 58, the anode 22 is shaped as a ring 59,and the means 13 for electron separation is shaped as a disk 60 set witha clearance "b" relative to walls 61 of the vacuum chamber 1. Aninterior space 62 of the ring 59 and an interior space 63 of thecylinder 58 are equal in cross-sectional area.

The holding fixture 48 for the product 47 under treatment is situated inthe interior space 63 of the cylinder 58. The disk 60 has a clearance"c" with respect to an end 64 of the cylinder 58. The interior space 63of the cylinder 58 is in fact the center hole 53 of the target 52 havingthe sputtering surface 57.

The aforementioned embodiment of the device is expedient to be used forintensifying the process of application of a wear-resistant coating tothe product 47 after its having passed the vacuum-plasma treatment, inparticular, chemical heat treatment, said coating consisting of thematerial the sputtering target 52 is made from.

As far as the process techniques involved in the vacuum-plasma treatmentis concerned, that is, preheating of the product under treatment and itsholding in a preset temperature range, the present embodiment of thedevice is similar to the preceding one.

The device, according to the invention, carrying into effect the methoddisclosed herein and presented in FIGS. 11 and 12 is similar to thedevice of FIG. 10.

The sole difference lies with the fact that the sputtering target 52(FIGS. 11 and 12) appears as a set of arcuate plates 66 insulated fromone another by insulators 65 and arranged circumferentially as shown inFIG. 12, thus establishing the center hole 53 of the sputtering target52 having the sputtering surface 57.

In the herein-described embodiment of the device the cross-sectionalarea of the interior space 62 (FIG. 11) of the ring 59 exceeds thecross-sectional area of the center hole 53 of the sputtering target 52.

The present embodiment of the device is reasonable to be used forobtaining high-quality hard coatings, since such a constructionarrangement of the target 52 reduces very much the danger of arcdischarges stricken on its surface and hence rules out the formation ofthe drop phase in the coating applied to the product 47.

The device presented in FIG. 13 is similar to that of FIGS. 1 and 4.

The sole difference resides in that provision is made in the device ofFIG. 13 for a source 67 of accelerated particles which is connected tothe vacuum chamber 1 and comprises a gas-discharge chamber 68accommodating a hollow cold cathode 69, an anode 70, a means 71 forpower supply of a discharge initiated in the gas-discharge chamber 68,said means 71 being connected to the cathode 69, the anode 70, and ameans 72 of an accelerating voltage having its negative pole connectedto the vacuum chamber 1. The source 67 is also provided with an emissiongrid 73 connected to the negative pole of a power supply source 74 whichin turn is connected to the means 72.

This embodiment of the device is expedient to be used for preheating theproduct 5 and its holding under a floating potential applied theretowith a view to enhancing the efficiency of the process of vacuum-plasmatreatment predominantly of products made from dielectric materials.

The mode of operation of the herein-disclosed device for treatment ofproducts in gas-discharge plasma which carries into effect the method,according to the invention, is as follows.

Air is evacuated from the vacuum chamber 1 (FIG. 1) by means of the pump(omitted in the drawing) through the connection 7 until a pressureestablished in the chamber 1 gets lower than the working pressure byabout one order of magnitude. Once the chamber 1 has been deaerated, theworking gas is admitted to fill the chamber. Considered hereinafter is aspecific embodiment of the herein-disclosed method as applied to thenitriding process which is most commonly used under industrialconditions in cases where nitrogen is employed as the working gas.Nitrogen in this particular case is fed from the source 6 of workinggas, its pressure being set within 10⁻² and 10 Pa.

A voltage is applied to the anode 3 and the integrally cold cathode 2from the source 9 of direct current. Then the cathode spot is initiatedon the cathode 2 with the aid of a vacuum-arc discharge initiationsystem (omitted in the drawing as being known conjointly and thereforenot being the subject of the present invention).

The cathode spot thus initiated moves over the working area 12 of thecathode 2, whereas the cathode spot cannot travel over the nonworkingarea 11 of the cathode 2 because the entire nonworking area 11 of thecathode 2 is covered by the shield 10 which is insulated from thecathode 2, thus precluding electric connection between the cathode 2 andthe anode 3 through the plasma column.

The plasma column generated by the cathode spot consists of metal ions(that is, the products of erosion of the material the cathode 2 is madefrom), which are ionized in the near-the cathode zone of the vacuum-arcdischarge and propagate away from the cathode 2 at a high velocity alongstraight line paths, and of electrons. Apart from metal ions the plasmacolumn incorporates the working gas ions which result from therecharging process upon colliding of the metal with the neutral workinggas molecules. Inasmuch as the metal ions propagate along straight linepaths, and the electron separation means 13 is interposed between thecathode 2 and the anode 5, the metal ions are held back on the V-shapedplates 14 and get condensed thereon. The electrons of the metal gaseousplasma are activated by the electric field of the anode 3 which passesthrough the gaps between the V-shaped plates 14 of the means 13 to maketheir way from the compartment 17 of the chamber 1 containing themetal-gaseous plasma to the compartment 18 thereof so as to ionize theworking gas contained in said compartment and establish the gaseousplasma through which the vacuum-arc discharge current is free to pass.

Thus the means 13 is essentially a boundary between two physicallydissimilar regions, that is, the region of the metal-gaseous plasmafilling the compartment 17 of the chamber 1 and the region of puregaseous plasma filling the compartment 18 of the chamber 1.

A peculiar feature of the vacuum-arc discharge is the fact that theelectron currents of such a discharge are limited only to thethermophysical properties of the integrally cold cathode 2. It is knowncommonly that to provide a vacuum-arc discharge current magnitude of afew hundreds or even thousands amperes is readily attainable. With suchhigh current intensity values the gaseous plasma in the compartment 18of the chamber 1 features a high degree of ionization (of the order of afew tens percent) and therefore high activity.

The surface of the anode 3, i.e., the product 5 under treatment isheated as a result of electron bombardment said surface is exposed to.The temperature of the surface is monitored with the aid of thethermocouple 19 made fast on the product 5. Once the working temperatureof the product 5 has been attained, the discharge current intensity isreduced to a value at which the power developed on the anode 3 getsequal to the amount of heat withdrawn from the product 5 (both throughheat radiation and transfer). It is at such a current that the product 5is held in a preset temperature range during which the surface layer ofthe product 5 is saturated with the working gas, that is the process ofthe vacuum-plasma treatment, in particular, chemical heat treatment iscarried out. The lower limit of the vacuum-arc discharge current is aminimum current of a stable persistence of such a discharge below whichthe discharge proceeds but unstably. For the cathode 2 made of diversematerials such a current is of the order of tens of amperes. That is whythe device, wherein the anode 3 is in fact the product 5 (which isconstructionally the simplest one) is applicable for vacuum-plasmatreatment of relatively robust products featuring considerable rate ofheat withdrawal at working temperatures. Conduct of vacuum-plasmatreatment at a positive potential is advantageous in that electronbombardment of the surface of the product 5 is not causative of surfacesputtering, therefore the product 5 subjected to such a vacuum-plasmatreatment preserves the initial quality of surface finish. This of primeimportance whenever the vacuum-plasma treatment, in particular, chemicalheat treatment is carried out of such products that are provided with athin-film cuating applied to their surface, which may be partly or evenfully destructed by ionic bombardment (that is, under a negativepotential applied to the product).

The device illustrated in FIG. 2 and carrying into effect the method,according to the invention, wherein the product 5 is held in a presettemperature range both at a positive and floating potential, is freefrom any restrictions imposed on carrying out the treatment of productsregardless of their weight.

The device operates as follows.

The product 5 is preheated by applying a positive potential thereto,which is supplied from the source 9 of direct current. The two-wayswitch 23 is in the position I, as soon as the temperature of theproduct 5 reaches the preset value the control unit 24 shifts thetwo-way switch to the position II, wherein the discharge anode is infact the anode 22, while the product 5 is under a floating potential.Since the vacuum-arc discharge current retains its initial value afterthe discharge has passed from the anode 3 to the anode 22, thegas-discharge plasma retains its activity at an unaffected level. Thismakes the present construction of the device favorably comparable withthe construction shown in FIG. 1, wherein the temperature control of theproduct 5 is effected due to reduction of the discharge current andhence of the rate of the process of vacuum-plasma treatment.

The device of FIG. 2 can be applied in the same way as the device orFIG. 1 but with the two-way switch 23 in the position I.

The graphic chart presented in FIG. 14 represents the efficiency of theprocess of vacuum-plasma treatment carried out using the deviceillustrated in FIG. 2.

There is carried out nitriding of the product 5 made of high-speed toolsteel having the following chemical analysis (in wt. %): W, 6.1, C, 0.8,Mo, 5.1; Cr, 4.0; Va, 1.8; Fe being the balance.

The product 5 is preheated by applying a positive potential thereto andheld in a preset temperature range under a combination of a positive anda floating potential. The temperature of the product 5 is maintained ata preset level by changing the two-way switch 23 over from the positionI to the position II, and vice versa. The parameters of the processvacuum-plasma treatment, the chemical heat treatment in this particularcase, are as follows: partial nitrogen pressure, 8×10⁻² Pa; vacuum-arcdischarge current, 120 A, voltage between the anodes 3, 22 and thecathode 2, 60 V, period of holding at 400° C., 35 min, at 500° C., 35min.

The graphic chart shown in FIG. 14 represents microhardness Hu of thenitrided layer in mPa (plotted against X-axis) versus the depth "h" ofthe layer in microns (plotted against Y-axis for two temperatures, i.e.,400° C. (curve "d") and 500° C. (curve "e").

The device of FIG. 2 is expedient to be used for vacuum-plasma treatmentof small-size products when preheating and holding are carried out at afloating potential applied to the product 5. In this case the two-wayswitch 23 is in the position II, and the vacuum-arc discharge parameters(i.e., current and voltage values) are selected to be such that thetemperature of the product 5 is not to exceed the value preset accordingto the treatment procedure.

With such a procedure of preheating and holding the product in a presettemperature range, the temperature of the product can he maintained at adegree of accuracy quite adequate for industrial practice by keeping thevacuum-arc discharge parameters constant at a required level, wherebythe use of temperature monitoring means can be dispensed with.

In the device of FIG. 3 the cathode 2 is made of such a material thatforms, upon a chemical reaction with the working gas, a wear-resistantmetal-containing compound, e.g., the cathode 2 may be made of titaniumwhich, when reacting with nitrogen, forms a stable wear-resistantcompound, that is, titanium nitride.

After carrying out the process of vacuum-plasma treatment of the product5 according to one of the aforementioned embodiments of the methoddisclosed herein, the means 13 made as a set of the V-shaped plates 14secured on the connecting rod 30, is raised, by means of the handle 31,to the socket 29. As a result, an unobstructed flight of metal ionsgenerated by the cathode 2 to the surface of the product 5 undertreatment is provided. Thus, a thin-film layer of a wear-resistanttitanium nitride compound is formed in t,e presence of the working gas,i.e., nitrogen, on the surface of the product 5 under treatment that haspassed the process of vacuum-plasma treatment, in particular, chemicalheat treatment.

An all-over treatment of cutting tools made from high-speed tool steelof the following chemical composition (wt. %): W 6.1, C, 0.8; Mo. 5.1,Cr, 4.0; Va, 1,8; Fe being the balance, comprising nitriding to form anitrided layer 15 to 25 um thick, followed by applying a wear-resistanttitanium nitride layer 4 um thick, increases wear-resistance of thetools by 150-300% compared with the cutting tools that have passedchemical heat treatment alone.

In the device of FIG. 4 the source 37 of direct current enables one tohold the product under treatment in a preset temperature range at anegative potential applied thereto. To this end, once the process ofpreheating the product 5 at a positive potential applied thereto hasbeen over, the two-position switch 23 is changed over to the positionII, that is, the discharge is transferred from the anode 3 to the anode22, and the holding fixture 4 of the product being treated is connected,by the switch 38, to the direct-current source 37. As a result, ahigh-voltage negative potential is applied to the product 5, whichcauses the ions of the gaseous plasma to accelerate towards the surfaceof the product 5 so as to perform the vacuum-plasma treatment, inparticular, chemical heat treatment, of said surface.

The examples giyen below illustrate the advantages of the methoddisclosed herein and carried into effect by the device of FIG. 4.

There is carried out nitriding of the surface of the product 5, i.e., atool provided with a film coating. Such a nitriding procedure is carriedout through the aforesaid coating, because the best adhesion of titaniumnitride layer to the tool base metal, i.e., high-speed tool steel isattained.

A lot of the products 5, that is, high-speed tool steel tips for cuttingtools has been subjected to nitriding, the chemical composition of saidhigh-speed tool steel being as follows (wt. %): W, 6.1; C, 0.8; Mo, 5.1,Cr, 4.0, Va, 1.8, Fe being the balance.

In the device of FIG. 4 the tips under treatment have preliminarily beencoated with titanium nitride layer 4 μm thick, said coating beingapplied with the slats of louverboards of the means 13 open in order toadmit metal ions generated by the integrally cold cathode 2 to passfreely to the surface of the product 5 under treatment. Then the slatsof the louverboards of the means 13 are closed and one lot of the tips20 in number is subjected to chemical heat treatment by being preheatedat a positive potential and held in a preset temperature range by acombination of a positive and a floating potential applied thereto, thetreatment parameters being as follows: working gas partial pressure,8×10⁻² Pa; vacuum-arc discharge current, 120 A; voltage between theanodes 3, 22 and the cathode 2, 60 V; temperature of the tips undertreatment, 500° C.; nitriding time, 40 min. The other lot of the tipsalso 20 in number is exposed to chemical heat treatment by beingpreheated at a positive potential and held in a preset temperature rangeby applying a negative potential to the tips under treatment, thetreatment parameters being as follows: partial nitrogen pressure, 8×10⁻²Pa; vacuum-arc discharge current, 60 A; voltage between the cathode 2and the anode 22, 60 V; temperature of the tips under treatment, 500°C.; negative voltage applied to the tips and supplied from the source37, 800 V; nitriding time, 40 min. A visual inspection of the two lotsof tips has found that the cutting edges of the tips of the second lotup to 2 mm which are devoid of the titanium nitride coating, which isdue to concentration of the ion stream at the cutting edges that causescathode sputtering of the titanium nitride layer. The tips thus treatedhave been tested by turning the steel having the following chemicalcomposition (wt. %): C, 0.36; Si; 0.2; Mn 0.5; Cr, 1.1; Fe being thebalance, with the following cutting speeds and feeds:

cutting speed--60 m/min,

rate of feed--0.63 mm/rev,

cutting depth--1 mm.

Average wear resistance (endurance) of the lot of tips that have beentreated with a combination of a positive and a negative potentialincreases by 6.7 times compared to the initial one, whereas the wearresistance of the tips that have been treated with a negative potential,increases by 2.3 times.

The example cited above gives a clear-cut illustration of the fact thatchemical heat treatment of products provided with a thin-film coatingusing the routine procedure involving the application of a negativepotential to the product under treatment is unpractical.

In the device of FIG. 4 there has been performed hardening of theproducts 5, that is, drills 1.8 mm in diameter, under a floatingpotential applied thereto. A lot of drills 50 in number is used, thedrills being clamped in the holding fixture 4 and subjected to nitridingwith the following treatment parameters: partial nitrogen pressure,6.5×10⁻¹ Pa; discharge current, 120 A; temperature of the product, 500°C.; time for preheating the drills to 480° C. under a floatingpotential, 12 min; time of holding at 480° C., 12 min.

The drills thus treated have been tested by drilling holes in steel ofthe following chemical composition (wt. %): C, 0.36; Si 0.2; Mn, 0.5;Cr, 1.1, Fe being the balance, under the following conditions:

drill spindle speed 8430 rpm,

length of feed per drill spindle revolution--0.043 mm,

drilling depth--4 mm.

An average increase in wear resistance: of the drills is 180%.

In the device of FIG. 5 the metal ions generated upon initiation of avacuum-arc discharge between the cathode 2 and the anode 3 andpropagated from the working area 12 of the cathode 2 along straight linepaths, do not get into the compartment 18 of the interior space of thechamber 1.

In the device of FIG. 6 the ion stream of the metal-gaseous plasma doesnot go beyond the limits of a solid angle equal to 180° and having itsvertex at the center of the cathode 2, whereby metal does not get ontothe product 5 under treatment.

In the device of FIG. 7 vacuum-plasma treatment of products is carriedout with the cathode 2 assuming the position shown with a dotted line inFIG. 7. With such a position of the cathode 2, the process ofapplication of hardening coatings made from the material of the cathodecan also be carried out adequately efficiently in the interior space ofthe chamber 1 bounded by a solid angle of 180°.

In the device of FIG. 8 the electric field inside the interior 46 of thehollow cylinder 44 is directed normally to the axis thereof due to theprovision of the disk 50 having the center hole 51 and of the hollowcylinder 44 (serving as the anode 22) whose end 45 is directed towardsthe integrally cold cathode 2. The solenoid 49 encompassing the anode 22generates an axially symmetrical magnetic field.

Thus, the electric and magnetic fields in the interior 46 of the hollowcylinder 44 are directed at right angles to each other.

It is common knowledge that the azimuthal electron Hall current arisesin the gaseous plasma placed in a radial electric field and an axialmagnetic field crossing each other. It is due to the appearance of theelectric Hall current that the electron path is extended and itslifetime is prolonged whereby the ionizing capacity of electronsincreases and hence the degree of gaseous plasma ionization is enhanced.Such an increase in the degree of plasma ionization gives rise to thefollowing two important consequences:

increased activity of the gaseous plasma which in turn leads tointensification of the process of vacuum-plasma treatment; and

higher proportion of electrical energy transferred from the vacuum-arcdischarge to the gaseous plasma which in turn increases the heatingcapacity thereof utilizable when the product under treatment ispreheated and held in a preset temperature range are carried out under afloating potential applied thereto.

In the device of FIG. 8 there have been performed two variants ofnitriding the product 47 made from high-speed tool steel having thefollowing chemical composition (wt. %): W, 6.1; C 0.8; Mo, 5.1; Cr, 4.0;Va, 1.8; Fe being the balance.

According to the first variant the product 47 is nitrided with thesolenoid 49 deenergized, that is, the nitriding procedure differs innothing from that effected in the device of FIGS. 1-7. The parameters ofthe nitriding process are as follows: partial nitrogen pressure,133,×10-1 Pa; vacuum-arc discharge current, 60 A; current of solenoid 49is such as to establish a voltage of 80 V between the cathode 2 and theanode 22; time for forming 15 μm thick nitrided layer, 12 min.

Thus, the presence of crossed electric and magnetic fields in thegas-discharge plasma in the device of FIG. 8 intensifies thevacuum-plasma treatment procedure.

The device of FIG. 9 is featured by all of the advantages possessed bythe device of FIG. 8 and apart from this, it has extended processingcapabilities of applying a wear-resistant coating to the surface of theproduct that has been subjected to vacuum-plasma treatment, inparticular, chemical heat treatment. To this aim, the sputtering target52 (the disk 54) is made from the metal of the wear-resistant coating tobe applied. When a high-voltage negative potential is applied to thesputtering target 52, its sputtering surface 57 facing towards thegas-discharge plasma is subjected to ion bombardment and is thussputtered. The sputtered material is deposited upon the product 47 toform a wear-resistant coating. When applying such a coating use is madeof a gaseous mixture consisting of argon and nitrogen as the workinggas.

Thus, the device of FIG. 9 can be used for carrying out a complexhardening process comprising chemical heat treatment followed byapplying a hardening coating, which adds to a great extent to thewear-resistance of the product 47.

The device of FIG. 10 enables one to carry out and intensify the processof applying a coating to the product 47 that has been passed avacuum-plasma treatment, in particular, chemical heat treatment, as wellas to attain more uniform application of the coating as for thickness.

In this embodiment of the device a positive column of the vacuum arcdischarge plasma runs along the internal surface of the cylinder 58. Thecross-sectional area of said discharge is approximately the samethroughout its pathway along the cylinder 58, which provides forconstant density of the ion current on the cylinder 58 along its wholelength and hence a homogeneous coating is ensured lengthwise thelong-sized product 47 located in the interior space 63 of the cylinder58.

The treatment process carried out in this embodiment of the devicedisclosed herein features the following parameters: argon pressureinside the chamber 1,5×10-2 Pa; discharge current, 100 A; voltagebetween the anode 22 and the cathode 2, 45 V; voltage on the target,1000 V, current in the circuit of the target 52, 14 A.

The rate of application of the titanium coating to the product 47 spaced50 mm apart from the target 52:

3.2 μm/h with the product 47 positioned in the lower portion of thetarget 52 as viewed in the direction of the election current of theplasma;

3.7 μm/h with the product 47 set in the central portion of the target52;

3 μm/h with the product 47 situated in the upper portion of the target52 as viewed in the direction of the electron current of the plasma.

Thus, the maximum coating inhomogeneity along the axis of the product 47is 19%.

The device of FIGS. 11 and 12 is instrumental in carrying out andintensifying the process of coating application to the products 47 thathave passed a vacuum-plasma treatment, in particular, chemical heattreatment, making it possible to enhance the quality of the coatingbeing applied as for thickness thereof, which is due to assured rulingout of the onset of the drop phase during sputtering of the target 52.This is provided by the construction arrangement of the target 52 asshown in FIG. 12. Provision of the target 52 in the form of the arcuateplates 66 insulated from one another reduces the danger of arcdischarges arising on its surface and hence excludes any possibility ofappearing metal drops during sputtering of the target 52. Otherwise theoperation of the device of FIGS. 11 and 12 is similar to that of thedevice of FIG. 10.

The device of FIG. 13 makes it possible to carry out and intensify theprocess of coating application to the products that have passed avacuum-plasma treatment, in particular, chemical heat treatment, and toadd to adhesive properties of the coatings being applied.

An accelerated beam from the source 67 is directed onto the surface ofthe product 5 under treatment in order to clean, activate, and preheatsaid surface. Said beam features highly homogeneous density of the fluxof accelerated particles across its cross-sectional area, thus uniformlycleaning the surface of the product 5 and additionally heating it, whichaugments the quality of the coatings applied subsequently thereto.

In addition, there is provided cleaning and preheating of dielectricproducts with a beam of fast neutral molecules resultant from rechargingof ions and/or with a beam of positive ions whose charge is neutralizedon the surface of the dielectric product by the electrons from thevacuum-arc discharge plasma.

A broad range of diverse embodiments of the herein-disclosed method fortreatment of products in gas-discharge plasma and carried into effect bythe device, according to the invention, makes it possible to effect anintense vacuum-plasma treatment of products under large-scale industrialconditions, followed by application of hardening coatings within therange of reduced pressures (10⁻² -10 Pa).

In the device disclosed herein and carrying into effect the method,according to the invention, the products under treatment are efficientlyheated and their temperature is maintained in a preset range by applyinga positive or a floating potential thereto. It is common knowledge thatelectron bombardment of the surface of the product under treatment doesnot affect the initial quality of surface finish; that is why thevacuum-plasma treatment under a positive potential involves no furthertechnological procedures, such as grinding and polishing.

Possibility of carrying out an intense process of vacuum-plasmatreatment under a floating potential without applying voltage to theproduct under treatment enables said process to be performed withouttemperature monitoring of the products under treatment, which is quiteessential in treatment of small-size products, such as drills having adiameter under 3 mm, where the temperature measurement process isdifficult to perform and, first and foremost, makes it possible to avoidannealing of sharp edges of the product due to an increasedconcentration of charged particles bombarding the surface of such edgesupon applying a voltage to the products under treatment. Carrying out ofthe process of vacuum-plasma treatment under a positive potential makesit possible to rule out the danger of arc discharges arising on thesurface of the products under treatment (that is, initiation of cathodespots on the products which in turn enables the process of vacuum-plasmatreatment to he conducted at an optimum rate independent of the dangerof initiation of the cathode spots on the surface of the product, saidspots being causative of erosion of said surfaces. Thus, the time spentfor carrying out the process of vacuum-plasma treatment is cut down,since there is no longer necessary to preheat the products undertreatment gradually for fear of initiation of the cathode spots ofvacuum-are discharge thereon.

It is noteworthy that unipolar arcs are likely to occur on the surfaceof the products under treatment under a floating potential appliedthereto. However, the appearance of such arcs is much less probable thanin case of a high-voltage negative potential. Endurance of cutting toolstreated according to the disclosed method increases substantially, e.g.,by 200-600% for tools used for turning hardly machinable steels, up to1000% for drills, and up to 300% for hobs.

The device carrying the herein-disclosed method into effect featureshigh reliability because the integrally cold cathode therein is heatedto a temperature as low as 300°-400° C.

Moreover, the device carrying into effect the method disclosed herein iscapable of producing gaseous plasma featuring a higher degree ofionization and hence more chemically active, whereby the time forformation of hardened surface layers is reduced.

The device carrying into effect the process disclosed herein is capable,apart from carrying out preheating, cleaning, and chemical heattreatment procedures, also of performing the processes of applyingthin-film coatings, inasmuch as the integrally cold cathode of thevacuum-arc discharge intended for emission of electrons which initiatethe gas-discharge plasma, can also serve as a source of an evaporablemetal from which the thin-film coating is made. The processes areperformed within the same pressure range of the working gas. As a resultof an all-over treatment of, e.g., cutting tools their enduranceincreases by 150-300%.

INDUSTRIAL APPLICABILITY

The device for treatment of products in gas-discharge plasma carryinginto effect the method for treatment of products in gas-dischargeplasma, can find application in mechanical engineering for hardening themachine elements to increase their wear resistance, in the tool-makingindustry for hardening diverse cutting tools, such as turning tools,milling cutters, hobs, drills, broaches, die sets, as well as inchemical engineering for making equipment designed to operate incorrosive media.

We claim:
 1. A method for treatment of products in a gas dischargeplasma, comprising the steps of:initiating a vacuum arc dischargebetween an anode and a cold cathode, said discharge featuring ametal-gaseous plasma and a gaseous plasma, both of said plasmas beingsubstantially isolated from each other by means that is substantiallyimpermeable to metal ions and permeable to electrons; establishing thegaseous plasma of the vacuum arc discharge by ionizing a working gaswith electrons separated from the metal-gaseous plasma of the vacuum arcdischarge using said means impermeable to metal ions and permeable toelectrons; and vacuum-plasma treatment of a product by preheating saidproduct to a working temperature and by holding the product in a workingtemperature range in the medium of the working gas.
 2. A methodaccording to claim 1, wherein the step of vacuum-plasma treatment of theproduct by preheating and holding the product in a working temperaturerange is carried out in the gaseous plasma of the vacuum arc discharge.3. A method according to claim 1, wherein the step of preheating of theproduct to working temperature is carried out by applying a positivepotential to the product.
 4. A method according to claim 1, wherein theproduct is held in a working temperature range by applying a positivepotential to the product.
 5. A method according to claim 1, wherein theproduct is additionally treated with a directional beam of acceleratedparticles.
 6. A method according to claim 5, wherein a directional beamof neutral particles is used as the directional beam of acceleratedparticles.
 7. A method according to claim 1, wherein after the producthas been preheated and held in a working temperature range in thegaseous plasma, a coating is deposited onto the surface of the productin the metal-gaseous plasma.
 8. A method according to claim 1, whereinafter the product has been preheated and held in a working temperaturerange in the gaseous plasma, a coating is deposited onto the surface ofthe product in the gaseous plasma using gas ion sputtering of targetslocated in the gaseous plasma.
 9. A device for treatment of products ina gas discharge plasma said discharge plasma comprising a metal gaseousplasma of metal ions, gas ions and electrons and a gaseous plasma of gasions and electrons, comprising:a source of direct current electricallyconnected to a cold cathode and to an anode; both the cold cathode andthe anode being enclosed in a vacuum chamber in a medium of a workinggas at a reduced pressure; and a means substantially impermeable tometal ions and permeable to electrons for separating from themetal-gaseous plasma electrons establishing the gaseous plasma byionizing the working gas.
 10. A device according to claim 9, wherein thesource of direct current is electrically connected to the anode, thecathode, and the chamber.
 11. A device according to claim 10, whereinthe vacuum chamber is used as an intermediate anode.
 12. A deviceaccording to claim 9, wherein the products are used as the anode.
 13. Adevice according to claim 9, wherein the means for separation ofelectrons is reciprocatingly movable with respect to the vacuum chamber.14. A device according to claim 9, wherein the means for separation ofelectrons appears as a set of V-shaped plates facing with one of theirside surfaces towards the cold cathode and with the other side surfacetowards the anode.
 15. A device according to claim 9, wherein a wall ofthe vacuum chamber is used as the means for separation of electrons,said wall being situated in a zone of the cold cathode which ispositioned so that its evaporative surface faces towards the wall.
 16. Adevice according to claim 15, wherein the cold cathode is so positionedthat its evaporation surface is angularly displaceable through 180° withrespect to the wall of the vacuum chamber being used as the means forseparation of electrons.
 17. A device according to claim 9, whereinprovision is therein made for a target connected to the negative pole ofan individual source of direct current and interposed between the meansfor separation of electrons and the anode.
 18. A device according toclaim 17, wherein the target is made in the form of a hollow cylinder.